The present invention relates to a cordless telephone which includes a portable unit and a fixed unit and, more particularly, to a cordless telephone with a capability of saving a battery of a portable unit while it is charged.
A portable unit included in a cordless telephone is usually provided with a rechargeable battery therein. A fixed unit includes a charging section with an altenative current-to-direct current (AC/DC) conversion function which is connected to a commercial AC power source and plays two different roles, i.e., converting an AC voltage to a DC voltage and feeding the DC voltage to the fixed unit and charging the battery of the portable unit. When the portable unit is loaded in the fixed unit, the battery of the portable unit is charged via charge terminals. A separate charger is sometimes used in place of the charging section of the fixed unit. This kind of cordless telephone is disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 62-81135 (Kato et al). This Laid-Open Patent Publication was assigned to the applicants including the applicant of the instant application and laid open Apr. 14, 1987, a corresponding U.S. application being issued Feb. 16, 1988 as U.S. Pat. No. 4,726,052.
The cordless telephone system of Kato et al determines whether a portable unit is being charged and, if it is being charged, conditions a transmitter for a waiting mode automatically, resulting in increasing the radio channel efficiency. However, such a cordless telephone system is not provided with any implementation for saving the battery of the portable unit.